Selective coherent phonon-mode generation in single-wall carbon nanotubes

Abstract

The pulse-train technique within ultrafast pump-probe spectroscopy is theoretically investigated to excite a specific coherent phonon mode while suppressing the other phonon modes generated in single-wall carbon nanotubes (SWNTs). In particular, we focus on the selectivity of the radial breathing mode (RBM) and the G-band for a given SWNT. We find that if the repetition period of the pulse train matches with the integer multiple of the RBM phonon period, the RBM amplitude can be maintained while the amplitudes of the other modes are suppressed. As for the G-band, when we apply a repetition period of a half-integer multiple of the RBM period, the RBM can be suppressed because of destructive interference, while the G-band still survives. It is also possible to keep the G-band and suppress the RBM by applying a repetition period that matches with the integer multiple of the G-band phonon period. However, in this case we have to use a large number of laser pulses having a property of "magic ratio" of the G-band and RBM periods.

Controlling Three Laser-Excited Coherent Phonon Modes in Boron Nitride Nanotubes To Produce Ultrashort Shaped Terahertz Pulses: Implications for Memory Devices

“…11 By optimization of the repetition rate of a pulse train, it was theoretically predicted to selectively excite the radial breathing mode or the G-band phonon mode in a single-walled carbon nanotube. 12 In addition, selective excitation of two nondegenerate lattice vibrations has been demonstrated in a variety of crystalline systems. 13−15 Moreover, in bismuth, the control of both the amplitudes and the phases of two coherent phonons has been achieved and visualized.…”

“…So far, one- and two-dimensional control have been achieved using ultrashort optical pulses: In single-walled carbon nanotubes (CNTs), the radial breathing mode of tubes with a specific diameter has selectively been excited using pulse trains, , and the dynamics along two phonon coordinates following a single laser pulse has been observed . By optimization of the repetition rate of a pulse train, it was theoretically predicted to selectively excite the radial breathing mode or the G-band phonon mode in a single-walled carbon nanotube . In addition, selective excitation of two nondegenerate lattice vibrations has been demonstrated in a variety of crystalline systems. − Moreover, in bismuth, the control of both the amplitudes and the phases of two coherent phonons has been achieved and visualized .…”